Laser-driven white lighting system for high-brightness applications

ABSTRACT

A high-power, high-brightness lighting system for large venue lighting, which includes a laser diode as the excitation source and one or more phosphor materials placed at a remote distance from the laser source. The invention offers a lighting system with the advantages of high brightness, high efficiency, high luminous efficacy, long lifetimes, quick turn-on times, suitable color properties, environmental sustainability, and easy maintenance, which may allow for smart and flexible control over large area lighting systems with resulting savings in operating and maintenance costs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional under 35 U.S.C. Section 121 ofco-pending and commonly-assigned:

U.S. Utility patent application Ser. No. 14/448,426, filed on Jul. 31,2014, by Kristin A. Denault, Steven P. DenBaars and Ram Seshadri,entitled “LASER-DRIVEN WHITE LIGHTING SYSTEM FOR HIGH-BRIGHTNESSAPPLICATIONS,” attorneys docket number 30794.524-US-U1 (2013-951-2),

which application claims the benefit under 35 U.S.C. Section 119(e) ofco-pending and commonly-assigned:

U.S. Provisional Patent Application Ser. No. 61/860,619, filed on Jul.31, 2013, by Kristin A. Denault, Steven P. DenBaars and Ram Seshadri,entitled “LASER-DRIVEN WHITE LIGHTING SYSTEM FOR HIGH-BRIGHTNESSAPPLICATIONS,” attorneys docket number 30794.524-US-P1 (2013-951-1),both of which applications are incorporated by reference herein.

This application is related to the following co-pending andcommonly-assigned patent applications:

P.C.T. International Patent Application Serial No. PCT/US2013/057538,filed on Aug. 30, 2013, by Ram Seshadri, Steven P. DenBaars, Kristin A.Denault, and Michael Cantore, entitled “HIGH-POWER, LASER-DRIVEN, WHITELIGHT SOURCE USING ONE OR MORE PHOSPHORS,” attorneys docket number30794.467-WO-U1 (2013-091-2), which application claims the benefit under35 U.S.C Section 119(e) of United States Provisional Patent ApplicationSerial No. 61/695,120, filed on Aug. 30, 2012, by Ram

Seshadri, Steven P. DenBaars, Kristin A. Denault, and Michael Cantore,entitled “HIGH-POWER, LASER-DRIVEN, WHITE LIGHT SOURCE USING ONE OR MOREPHOSPHORS,” attorneys docket number 30794.467-US-P1 (2013-091-1), whichapplications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present invention relates generally to the field of solid-statewhite lighting devices and specifically to the field of high-brightnesslighting, in which there is a need to illuminate a large area. Inparticular, the invention embodies the generation of white light using alaser diode (LD) as the excitation source in combination with phosphormaterials for high-brightness applications.

2. Description of the Related Art.

Large area venues such as sports arenas, auditoriums, and parking lotsrequire a lighting system with high brightness, high luminous efficacy,and quality white light in terms of color rendition and colortemperature. The lighting system should additionally have the qualitiesof energy efficiency, simple and flexible operation and control, easyand low-cost maintenance, and environmental sustainability.

Most current high-brightness lighting systems use high intensitydischarge (HID) lamps, which are usually metal halide or high pressuresodium vapor lamps. These HID lamps are widely used for this applicationdue to their high luminous efficacy compared to fluorescent orincandescent lamps and longer operating lifetimes. A typical metalhalide lamp has a luminous efficacy of 65 lm/W to 115 lm/W with alifetime of 10,000 hours to 20,000 hours. The quality of the white lightproduced is also suitable for large venue applications with a colorrendering index (CRI) of 65 to 90 and a correlated color temperature(CCT) of 3000 K to 20,000 K. The HID light fixtures are typicallymounted at a distance above the venue and the output light is directedto illuminate the area below.

The use of HID lamps for high-brightness lighting applications currentlyposes a number of disadvantages. For one, the warm up time for the lampsto reach full brightness can take anywhere from 1 minute to 15 minutes.Additionally, if the lights are turned off, it can take up to 10 minutesbefore they can be turned on again. This cycling of restarting thelighting before they have sufficiently cooled is also a source of wearand leads to quicker degradation and shorter lifetimes. For this reason,large venue lighting is rarely turned off if the lights need only to beoff for a short amount of time. In this case, shutters are used to blockthe light, instead of turning the lights off. This is not an energyefficient means of operation since electricity is still being used bythe lights. The same situation occurs if only a section of lights is toremain on during an event. This operation technique therefore alsointroduces a shutter into the lighting system, which must also bemaintained and may require a motor for operation. The final disadvantageof HID lamps for large venue lighting concerns the maintenance.Replacement of lights requires manual replacement, and since the lampsare usually mounted at a height above the venue, this can be a dangeroustask.

With the advent of light emitting diode (LED) technologies, such aslaser diodes, new large venue lighting systems are being designed. Theseinclude the use of LEDs combined with a phosphor material to producewhite light. LED-based lamps offer similar benefits as HID lamps interms of luminous efficacies, color rendition, and color temperature.LED-based lamps also have the advantage of longer lifetimes up to 50,000hours, relatively instant turn-on times achieving full brightness inless than a microsecond, the ability to be turned off and on quickly,and environmental sustainability. An important advantage is thereforethat different sections of lights can be flexibly turned on and off atwill, eliminating the need for shutters and saving energy. Themaintenance problems still exist with LED-based stadium lighting as withHID lamps, such that replacement requires individual bulbs to be changedmanually.

There is therefore a need for large venue lighting that includes all ofthe benefits of prior systems including high-brightness, highefficiency, high luminous efficacy, long lifetimes, quick turn-on times,suitable color properties, and environmental sustainability with theadded advantage of easy maintenance. Such a system would allow for smartand flexible control over the lighting, ease of maintenance, and savingsin operating and maintenance costs. The present invention satisfies thisneed.

SUMMARY OF THE INVENTION

To overcome the limitations in the prior art described above, and toovercome other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosesa high-power, high-brightness lighting system for large venue lighting,comprising a laser diode as the excitation source and one or morephosphor materials placed at a remote distance from the laser diodesource.

The preferred embodiment of the invention comprises an UV or blue lightemitting laser diode as the excitation source, one or moredown-converting phosphor materials with an emission color in the visibleregion of the electromagnetic spectrum ranging from blue to red, astructure for housing the phosphor materials, and a waveguidingmaterial.

The laser diode may be placed at ground level of a large venue to allowfor easy maintenance and changing of the laser diode. Waveguidingmaterials, for example, optical fibers, may then be used to carry thelaser light to the phosphor materials. The laser diode may instead beplaced at a distance relatively closer to the point of illumination, butstill easily accessible to allow for maintenance, and directed onto thephosphor material without transmission through a waveguiding material.

The laser diode emission beam may be split into several beams directedtowards phosphor materials in different areas of the large venue. Thelaser beam may or may not be diffused before striking the phosphormaterials.

The structure for housing the phosphor material may be placed at thepoint of illumination. The structure for housing the phosphor materialmay consist of the phosphor material deposited onto a substratematerial, such as polished aluminum or a silver coating. The substratemay act as a reflector material. The substrate may act as a heat sink.The structure for housing the phosphor material may completely enclosethe phosphor material with an optically transparent window to direct theemitted white light towards the area to be illuminated. The near-UV orblue laser diode light may or may not be filtered out from the resultingwhite light through the use of long-pass filters, resulting in eye safedevices.

A lighting system which comprises laser diode excitation of a phosphormaterial offers many advantages to both HID and LED-based lightingsystems. LED-based lighting systems, which typically use an UV-emittingor blue-emitting LED combined with one or more phosphor materials,already offer benefits over HID lighting systems including longlifetimes, relatively instant turn-on times, the ability to be turnedoff and on quickly, environmentally friendly designs, and enormousenergy savings. Yet, the overall efficiency of these devices can stillbe improved.

One such example is to control the operating temperature of the device.When operating an LED, the temperature will inevitably increase, yet thephosphor particles exhibit a loss in efficiency as the temperature ofthe device increases. This temperature increase will also occur whenusing a laser diode as the excitation source, but using a thermallyconductive substrate can minimize the loss in efficiency of the phosphormaterials.

In addition, LEDs suffer from efficiency loss and color instability withincreased operating current, making high-power, high-brightness devicesnot achievable using current LEDs as the excitation source. In contrastto LEDs, laser diodes do not exhibit this efficiency loss with increasedoperating current, many exhibit increased efficiency as currentincreases, and maintain color stability. Using a laser diode allows forthe realization of a high-power solid state white lighting device withstable color properties and no loss in efficiency at high operatingcurrents.

Laser-based devices also offer easy servicing of parts. The use oflasers with a remote phosphor configuration allows the laser to beplaced at a relatively far distance from the phosphor, as would beuseful in the case of large venue lighting. Lasers on the ground level,which excite phosphors placed at the point that is to be illuminated,can then easily be serviced when necessary, in contrast to LED-basedlighting, where the entire LED device must be placed at the point ofillumination.

Overall, the invention described here may provide a stable lightingsystem with the advantages of high brightness, high efficiency, highluminous efficacy, long lifetimes, quick turn-on times, suitable colorproperties, and environmental sustainability with the added advantage ofeasy maintenance. Such a system may allow for smart and flexible controlover the lighting system, ease of maintenance, and savings in operatingand maintenance costs.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIGS. 1(a), 1(b) and 1(c) are schematics representing the laser diode.

FIGS. 2(a), 2(b), 2(c) and 2(d) are schematics representing the outerstructure for housing the phosphor material.

FIGS. 3(a), 3(b) and 3(c) are schematics representing the substrateinside of the structure for housing the phosphor material.

FIG. 4 is a schematic representing the lighting system in the context ofa large venue, using a stadium as an example.

FIGS. 5(a), 5(b), 5(c) and 5(d) are schematics representing the methodsfor transferring the laser diode excitation to the phosphor material.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Technical Description

FIGS. 1(a), 1(b) and 1(c) are schematic diagrams representing the laserdiode excitation source. The laser diode housed in casing 1 may emitlight 2 in the wavelength range from UV to blue. The laser diodeemission 2 will exit the laser diode casing 1. After the light 2 exitsthe casing 1, the light 2 may be transported to the phosphor materialdirectly through the atmosphere, as illustrated by FIG. 1(a), or by awaveguiding material 3, as illustrated in FIG. 1(b). The laser beam 2may also be transported to the phosphor material in the form of a singlebeam of light 2, as shown in FIG. 1(a), or first passing through adiffuser 4 to split the single laser beam into multiple beams of light2, as shown in FIG. 1(c). Several laser diodes may be used as multipleexcitation sources in order to allow for flexible control the lightingsystem, including the option to turn off certain sections while leavingother sections illuminated. The laser diode casings 1 may also be ableto pivot mechanically in order to change the direction of the emittedlight 2 to illuminate different section.

FIGS. 2(a), 2(b), 2(c) and 2(d) are schematic diagrams representing theouter structure 5 for housing the phosphor material to be excited. Thestructure 5 may be constructed in any number of different shapes, forexample, a square or rectangle, as illustrated in FIG. 2(a) and FIG.2(c), or a circle or oval, as illustrated in FIG. 2(b) and FIG. 2(d).The structure 5 may have an outer covering 6 to direct the emitted whitelight in a specific direction, as illustrated in FIG. 2(a) and FIG.2(b), or may not, as illustrated in FIG. 2(c) and FIG. 2(d). Thestructure 5 may or may not have a hinge 7 connecting the structure 5 toa post, which may move mechanically to adjust the angle. The structure 5may completely enclose the phosphor material to protect it fromenvironmental conditions and may have an optically transparent window 8from which the emitted white light exits the structure 5. Inside thestructure 5 may be a substrate 9 upon which the phosphor material isdeposited.

FIG. 3(a) is a schematic diagram representing the substrate 9 upon whichthe phosphor material is deposited. The substrate 9 may be made of athermally conductive material to transport heat generated away from thephosphor material to maintain high operating efficiencies. The surface10 of the substrate 9 may be reflective in nature, comprised of, forexample, polished aluminum or a layer of silver, to reflect the emittedwhite light down onto the area to be lighted. As illustrated in FIG.3(b) and FIG. 3(c), the surface 10 of the substrate 9 may have adeposited layer 11, which contains a mixture of the phosphor material12, which may be in powder form, encapsulated in an opticallytransparent matrix 13. The surface of the deposited layer 11 may betextured in a manner that promotes light extraction and effectivelymixes the light components to create a homogeneous white light. Thephosphor material 12 may be a combination of one or more phosphors ofdifferent compositions that emit light at different wavelengths in thevisible region of the electromagnetic spectrum.

FIG. 4 is a schematic representing the lighting system in the context ofa large venue, for example, a stadium 14. The area to be lighted isdescribed by 15 and the area where spectators reside is described by 16.The laser diode emission must not travel through the area wherespectators reside 16 due to eye safety concerns. The structures forhousing the phosphor material 5 may be placed above the stadium 14, withthe angle of reflected light being down towards the area to be lighted15. The laser diodes 1 may be placed at a height above the area wherespectators reside 17 or at ground level 18. Both locations 17 and 18would still be located in an area that is easily accessible for laserdiode 1 maintenance. If the laser diode 1 is placed at ground level 18,waveguiding material (not shown) must be used to carry the laser diodeexcitation to a location above the area where the spectators wouldreside 17.

FIGS. 5(a), 5(b), 5(c) and 5(d) are schematic representationsillustrating the methods for transferring the laser beam 2 from thelaser diode casing 1 to the structure 5 housing the phosphor material.FIG. 5(a) shows the laser diode casing 1 placed at a height above thearea where spectators reside 17 with the laser beam 2 directed into thestructure 5 housing the phosphor material, while FIG. 5(b) shows thesame configuration, but with the laser beam 2 passing through a diffuser4 before reaching the structure 5. FIG. 5(c) and FIG. 5(d) show thelaser diode casing 1, which may be placed either at a height above thearea where spectators would reside 17 or at ground level 18, with thelaser beam 2 carried through a waveguiding material 3 and then directedinto the structure 5 housing the phosphor material. The waveguidingmaterial 3 may transport the laser beam 2 either to a height above thearea where spectators reside 17, as shown in FIG. 5(c), or to thestructure 5, as shown in FIG. 5(d).

Conclusion

This concludes the description of the preferred embodiment of thepresent invention. The foregoing description of one or more embodimentsof the invention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be limited not by this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. A method for illuminating a venue with a whitelight source, comprising: using one or more laser diode sources thatemit light in a first wavelength range to excite one or more phosphormaterials that emit light in a second wavelength range; wherein thesecond wavelength range is longer than the first wavelength range andproduces white light; wherein a structure, having an opticallytransparent window, is provided for housing the phosphor material;wherein the structure completely encloses the phosphor material toprotect it from harsh conditions; wherein the structure comprises asubstrate upon which the phosphor material is deposited, and thesubstrate is made of a thermally conductive material to transport heatgenerated away from the phosphor material; wherein the light emittedfrom the laser diode sources enters the structure to interact with thephosphor material and light emitted from the phosphor material exits thestructure through the optically transparent window; wherein the phosphormaterials are placed at a point of illumination with the light emittedfrom the phosphor material being directed towards an area to be lighted;and wherein the laser diode sources are not placed at the point ofillumination but are placed at a location that allows for maintenance ofthe laser diode sources.
 2. The method of claim 1, wherein the lightemitted by the laser diode sources are transferred to the point ofillumination via direct emission or a waveguiding material.
 3. Themethod of claim 1, wherein the structure has a square, rectangular,circular or oval shape.
 4. The method of claim 1, wherein the structureis connected to a post with or without a hinge that allows for tilting.5. The device of claim 1, wherein the structure has an outer coveringthat directs the light emitted from the phosphor material in a specificdirection.
 6. The method of claim 1, wherein the optically transparentwindow further comprises a long-pass filter that filters out laserlight.
 7. The method of claim 1, wherein the substrate has a reflectivesurface to reflect the light emitted from the phosphor material onto thearea to be lighted.
 8. The method of claim 1, wherein the phosphormaterial is deposited on the substrate using an optically transparentmatrix.
 9. The method of claim 1, wherein the phosphor material is acombination of one or more phosphors of different compositions that emitlight at different wavelengths.
 10. The method of claim 1, wherein alayer containing the phosphor material is deposited on a surface of thesubstrate and a surface of the layer is textured to promote lightextraction and to mix light components to create a homogeneous whitelight.
 11. A device for illuminating a venue, the device comprising: alaser diode for emitting a first light; one or more phosphor materials,optically coupled to the laser diode, for emitting a second light whenexcited by the first light; and a structure, having an opticallytransparent window, for housing the phosphor materials, wherein: thestructure completely encloses the phosphor materials to protect themfrom harsh conditions; the structure comprises a substrate upon whichthe phosphor materials are deposited, and the substrate is made of athermally conductive material to transport heat generated away from thephosphor materials; wherein the first light emitted from the laser diodeenters the structure to interact with the phosphor materials and thesecond light emitted from the phosphor materials exits the structurethrough the optically transparent window; and the structure is placed ata remote distance from the laser diode at a point of illumination withthe second light emitted from the phosphor materials being directedtowards an area to be lighted.
 12. The device of claim 11, wherein thefirst light emitted by the laser diode is transferred to the point ofillumination via direct emission or a waveguiding material.
 13. Thedevice of claim 11, wherein the structure has a square, rectangular,circular or oval shape.
 14. The device of claim 11, wherein thestructure is connected to a post with or without a hinge that allows fortilting.
 15. The device of claim 11, wherein the structure has an outercovering that directs the second light emitted from the phosphormaterials in a specific direction.
 16. The device of claim 11, whereinthe optically transparent window further comprises a long-pass filterthat filters out laser light.
 17. The device of claim 11, wherein thesubstrate has a reflective surface to reflect the second light emittedfrom the phosphor materials onto the area to be lighted.
 18. The deviceof claim 11, wherein the phosphor materials are deposited on thesubstrate using an optically transparent matrix.
 19. The device of claim11, wherein the phosphor materials are a combination of one or morephosphors of different compositions that emit light at differentwavelengths.
 20. The device of claim 11, wherein a layer containing thephosphor materials is deposited on a surface of the substrate and asurface of the layer is textured to promote light extraction and to mixlight components to create a homogeneous white light.